Sensor and ink-jet print-head assembly and method related to same

ABSTRACT

The invention relates to a sensor and ink-jet print-head assembly comprised in a housing for a hand-held and hand-operated printing device controlled by a processor, and a method therefore. It provides a control for navigation with coordinate systems and angles on a print medium that preferably is bigger than the assembly.

This application is the U.S. national phase of international applicationPCT/SE02/01328, filed Jul. 3, 2002, which designated the U.S., theentire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention pertains to a sensor means and an ink-jetprint-head assembly for a hand-held and hand-operated printing on aprint medium controlled by a processor, and a method therefore, socalled Random Movement Printing Technology (RMPT). Specifically itprovides a new control to determine the position of the assembly on aprint medium.

BACKGROUND ART

Hand-held and hand-operated printing devices with an ink-jet print-headare known through various documents.

U.S. Pat. No. 5,927,872 by Yamada discloses a system and a method ofprinting an image represented by a frame of image data utilizing ahand-held printer having optical sensor means for tracking positions ofthe hand-held printer relative to the surface of a print medium during aprinting process. It is monitored in real time using navigationinformation generated by the optical sensor.

Each optical sensor comprises an array of opto-electronic elements tocapture images of the surface of a print medium at fixed time intervals.Preferably, the optical sensor means can detect slight patternvariations on the print medium, such as paper fibers or illuminationpattern formed by highly reflective surface features and shadowed areasbetween raised surface features.These features can then be used asreferences for determining the position and the relative movement of thehand-held printer. During the printing process, the printed portions ofthe image can also be used as reference positions by the hand-heldprinter.

In the preferred embodiment, the hand-held printer contains a navigationprocessor and a printer driver. Using the printer driver, the navigationprocessor drives the hand-held printer to print segments of the imageonto a print medium as the hand-held printer travels across the printmedium during a printing process. Each segment of the image is printedonto a particular location on the print medium to form a composite ofthe image.

In the U.S. Pat. No. 6,233,368 B1 by Badyal et al it is taught a CMOSdigital integrated circuit (IC) chip on which an image is captured,digitized, and then processed on-chip in substantially the digitaldomain.

A preferred embodiment comprises imaging circuitry including a photocell array for capturing an image and generating a representative analogsignal, conversion circuitry including an n-bit successive approximationregister (SAR) analog-to-digital converter for converting the analogsignal to a corresponding digital signal, filter circuitry including aspatial filter for edge and contrast enhancement of the correspondingimage, compression circuitry for reducing the digital signal storageneeds, correlation circuitry for processing the digital signal togenerate a result surface on which a minima resides representing a bestfit image displacement between the captured image and previous images,interpolation circuitry for mapping the result surface into x- andy-coordinates, and an interface with a device using the chip, such as ahand-held scanner.

The filter circuitry, the compression circuitry, the correlationcircuitry and the interpolation circuitry are all embodied in an on-chipdigital signal processor (DSP). The DSP embodiment allows precisealgorithmic processing of the digitized signal with almost infinite holdtime, depending on storage capability. The corresponding mathematicalcomputations are thus no longer subject to the vagaries of CMOS chipstructure processing analog signals. Parameters may also be programmedinto the DSP's software making the chip tunable, as well as flexible andadaptable for different applications.

U.S. Pat. No. 5,644,139 by Allen et al discloses a scanning device and amethod for forming a scanned electronic image including the use ofnavigation information that is acquired along with image data, and thenrectifying the image data based upon the navigation and imageinformation. The navigation information is obtained in frames. Thedifferences between consecutive frames are detected and accumulated, andthis accumulated displacement value is representative of a position ofthe scanning device relative to a reference. The image data is thenpositioned-tagged using the position data obtained from the accumulateddisplacement value. To avoid the accumulation of errors, the accumulateddisplacement value obtained from consecutive frames is updated bycomparing a current frame with a much earlier frame stored in memory andusing the resulting difference as the displacement from the earlierframe. These larger displacement steps are then accumulated to determinethe relative position of the scanning device.

The above documents do only teach how to determine the position in aconceptual generation of navigation information. In this context theU.S. Pat. No. 5,927,872 by Yamada uses the navigation information for ahand-held scanner disclosed in U.S. Pat. No. 5,644,139 by Allen et al.The invention according to Allen et al teaches navigation throughcomparison of pixels on a frame basis.

By analyzing the state of the art through the above documents a need ofproviding a navigation control through a coordinate system emerges,which does not need to compare prior position information with currentposition information for a hand-held printer.

SUMMARY OF THE DISCLOSED INVENTION

The present invention relates to a new sensor and an ink-jet print-headassembly for a hand-held and hand-operated printing on a print mediumcontrolled by a processor and a method therefore. One aim of the presentinvention is to provide a new navigation control for print-outsaccomplished by the assembly.

Hence, the present invention sets forth a sensor and an ink-jetprint-head assembly comprised in a housing for a hand-held andhand-operated printing device controlled by a processor. Thereby itcomprises:

two position sensor means at least one sensor means being related to afirst coordinate system, having one axis in a relation to the print-headassembly, and one axis in a direction through both sensor means;

a print-head array attached in a fixed position to the sensor means;

input means on the housing connected to the processor for input ofcontrol commands;

determining means for reference coordinates in a second coordinatesystem provided in relation to a print medium, the reference coordinatesbeing established by a control command through the input means with thethus read sensor means signals;

integrating means for keeping track of the assemblies position relatedto the reference coordinates in the second coordinate system byintegrating displacement of sensor means position in the firstcoordinate system;

computing means for transforming the sensor means coordinates tocoordinates in the second coordinate system, whereby the assembliesposition on the print medium is determined in relation to the referencecoordinates.

In one embodiment of the present invention a look-up table comprisesnormalized sensor steps with a predetermined resolution between sensorsteps, one of the sensor steps determining a minimum movement of theassembly.

One embodiment comprises that a position is expressed through thecoordinates of the sensor means and the angle between the prior positionand the current position of the sensor means.

Another embodiment comprises that the transforming of the sensor meanscoordinates is derived through the position of the sensor means relatedto the first coordinate system and the angle of the print-head array inrelation to the second coordinate system.

A further embodiment comprises that an angular change is computed as thedifference of the sensor means movement in the y-direction of the firstcoordinate system multiplied with a constant which is determined inrelation to the distance between the two sensor means.

A still further embodiment comprises that the print-head nozzle positionis computed from the knowledge of the position of one sensor means andthe tilt angle of the assembly, by calculating the position of the firstand last nozzle in the array.

Yet one other embodiment comprises that remaining nozzle positions arecomputed by starting from the first nozzle positions and adding up thedifference in x- and y-directions between the nozzles, whereby the x-and y-distance between the first and last nozzle is divided by thenumber of nozzles.

A yet further embodiment comprises that its width is smaller then thewidth of the print medium.

A still further embodiment comprises that a positioning means isprovided to position the assembly in a correct starting position inrelation to the print medium.

Yet another embodiment comprises that a, not visible for a human eye,pattern provided by injected ink-jet drops in even intervals is used asreference points to adjust for possible sensor means positiondislocations.

Furthermore the present invention sets forth method for a sensor andink-jet print-head assembly comprised in a housing for a hand-held andhand-operated printing device controlled by a computer processor. Itcomprises the steps of:

providing two position sensor means, whereby at least one sensor meansbeing related to a first coordinate system, having one axis in arelation to the print-head assembly, and one axis in a direction throughboth sensor means;

providing a print-head array attached in a fixed position to the sensormeans;

providing input means on the housing connected to the processor forinput of control commands;

providing determining means for reference coordinates in a secondcoordinate system provided in relation to a print medium, the referencecoordinates being established by a control command through the inputmeans;

providing integrating means for keeping track of the assemblies positionrelated to the reference coordinates in the second coordinate system byintegrating displacement of sensor means position in the firstcoordinate system;

providing computing means for transforming the sensor means coordinatesto

coordinates in the second coordinate system, whereby the assembliesposition on the print medium is determined in relation to the referencecoordinates.

The method of the present invention is able to perform method steps ofthe above assembly embodiments in accordance with attached methodsub-claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Henceforth reference is had to the accompanying drawings for a betterunderstanding of the given examples and embodiments of the presentinvention, wherein:

FIG. 1 illustrates a perspective view in section of a printing deviceaccording to the present invention;

FIG. 2 illustrates a perspective view from underneath of a printingdevice according to the present invention;

FIG. 3 illustrates a schematic view of the main components of a printingdevice according to the present invention;

FIG. 4 illustrates a perspective view of another embodiment for aprinting device according to the present invention;

FIG. 5 illustrates a perspective view of a simpler printing deviceaccording to the present invention;

FIG. 6 illustrates a sensor/print-head assembly in accordance with thepresent invention;

FIG. 7 illustrates a diagram with parameters used to determine theposition of a sensor in accordance with the present invention;

FIG. 8 illustrates a diagram with parameters for the print-head nozzleposition in accordance with the present invention.

FIG. 9 illustrates an image to be print out; and

FIG. 10 illustrates a part random print out of the image with theprinter according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention discloses a hand-held printer device, whichsubstitutes both the mechanical control of a print-head and forwardfeeding of a print-out through hand movements on a printing surface.This enables a manufacturing of a printer device, having less width thanthe actual print-out, and a reduction of the total of mechanicalcomponents in its construction.

It is designed to provide a compact portable printing device in order toenable a user to print from small portable devices such as a cellularphone, a portable PC, a personal digital assistance (PDA) or the like,and other portable electronic devices or for electronic stamping,printing of small texts, tags, addresses, cutting and clipping.

By fixing a print-head in a construction plate where one or morepositioning sensor means are fixed as well, it is possible to obtain ageometrical construction with an x- and y-coordinate system and toestablish, with great mathematical accuracy, the coordinates x and y foreach individual ink-jet opening/nozzle in the print-head.

The coordinates, during a time frame, constitute the grounds for anaccurate and precise spraying of ink-drops onto a printing surfaceaccording to a predetermined printing design. Even when the coordinateschange over a time period, it is possible to calculate in real time, thechanges in direction, speed, acceleration, rotation etc. along thez-axis controlled by a microprocessor. It provides the possibility toadjust the printing-head to spray an even and pre-programmed flow ofink-jet drops into an adjustable and varying flow of ink-jet drops.

FIGS. 1 and 2 illustrate a hand operated printing device composed by aconstruction/design body 1 and a print-head 2 which interact with one ormore optical positioning sensor means 3, a micro controller circuit 4, acommunication unit 5 to transmit the data, one or more command buttons 6a control screen, and a source of energy, in this case a battery 8.

The embodiment according to FIGS. 1 and 2 illustrate the differentcomponents of a printing device fixed to a printed circuit card whichsimultaneously functions as a construction surface where thosecomponents are fixed. An elevation in the construction secures that thelowest surface of the printing device does not touch the area where theink has been previously applied provided that the printing device isremoved from that area.

The printing process starts with a data file containing pre-selectedprinting patterns, which are sent via the communication unit 5 to a datamemory, for example, one which is built into the micro controllercircuit 4. With the assistance of a built-in positioning means 13 andone of the command buttons 6, the coordinates are indicated to anoutgoing point of reference in the printing surface. One or more sourcesof light, for example light emitting diodes (LED), lighting up theprinting frame so that the optical positioning sensor means 3 areactivated and then the forward feeding of the coordinates to the microcontroller circuit can take place.

When the positioning sensor means 3 and the print-head 2 are fixed inrelation to each other, a geometrical construction with all thenecessary parameters for a mathematical calculation of the coordinatesof the print-head 2 can be achieved.

The micro controller circuit 4 contains a software program, which usesthe incoming data from the positioning sensor means 3 and mathematicalequations to calculate in real time the coordinates for each individualink-jet nozzle 12.

Using the measures of two coordinates establishes the required movementdirection for each case. The time difference between two measurementsindicates the acceleration and speed required. Simultaneously allmeasurements and equations are compared with the stored printingcommands based upon coordinates equated from the original data file.

At this stage the micro controller circuit has sufficient information toseize a decision. On a positive indication an electric impulse isgenerated in the piezo- or termo-electrical micro pumps in the concernedink-jet nozzles 12, which in turn sends out ink-jet drops onto theprinting surface.

The printing commands are erased after each electric impulse so thateven if the ink-jet nozzles coincide with the previous coordinates noink drops are sent out to the existing print out.

FIG. 3 illustrates how the different components of the printing deviceinteract as well as reproduction of the geometrical forms establishedbetween the ink-jet nozzles 12 and the positioning sensor means 3.

The embodiment according to FIG. 4 illustrates the printing device witha complementary digital camera 14, for example, such as a CCD equippedcamera.

The print-head 2 can be pre-programmed to send out, with even intervalssmall groups of separated microscopic ink-jet drops pairs, which do notbelong to the actual printing pattern but which can build a recognizablepattern for the camera 14. The camera registers these dots and transmitsthe information onto the micro controller circuit 4 which uses theinformation as a reference for ongoing revision of the position of theprinting device and in that way reduce the effect of the margin of errorbuilt-in the positioning sensor means 3. This embodiment is especiallyeffective when printing on bigger surfaces as well as when theresolution and quality demands are high.

These groups of microscopic ink-drops are essentially invisible for thehuman eye and they do not affect the printing result in any noticeableway.

FIG. 5 illustrates another embodiment of the present invention forprinting of smaller text quantities or graphics.

This can be considered as an electronic labeling with a pre-programmedand/or programmable electronic stamp pad.

In this embodiment only one positioning sensor means 3 is used andaccordingly a simpler micro controller circuit 4 is needed, since theprinting device only makes smaller and relatively straight movements.

The sensor/print-head device consists of two position sensor means S0,S1 and a print head array 60 mounted together as FIG. 6 illustrates.FIG. 6 illustrates further, the two sensor means S0 and S1 in a fixedrelation to a print-head array 60 with ink-jet nozzles. Ho depicts thedistance from the array 60 to the sensor means S0, here Ho is the samedistance to the sensor means S1. Ve and Vo, indicate the distance to theupper most and the lover nozzle in the array 60, respectively. Thesensor means S0, S1 provide a signal corresponding to movements in x-and y-directions in a first coordinate system fixed to the respectivesensor means S0, S1. The sensor means S0, S1 are fixed so that theircoordinate systems are parallel to each other. A software keeps track ofthe assembly's position and angle relative to the paper coordinatesystem by integrating the movements given by the sensor means signals.

The new positions given the differential movements of sensor means S0,S1 are calculated as follows.

All position changes given in the sensor means coordinate system must betransformed to position and angle of the sensor system in a paper orother print medium coordinate system, here named as a second coordinatesystem. Since the distance, 2Ho, between the two sensor means is fixedit is enough to know the position of one sensor means and the angle ofthe print head array relative to the second coordinate system.

Illustrated in FIG. 7, is a movement or navigation of the sensorprint-head assembly according to FIG. 6. The array 60 has been moved ornavigated an angle alpha. The upper most nozzle is depicted as Pnlastand the lower nozzle as Pnfirst, respectively, in FIG. 7. Also, thesecond coordinate system is depicted with the two longer arrow axis inFIG. 7.

In FIG. 7 at least one of the sensor means is assigned a firstcoordinate system, whereby one axis 62, preferably the x-axis, isdirected through both sensor means S0, S1, and the other axis,preferably in a relation to the array 60, here in parallel to the array.

In FIG. 8, the same movement as in FIG. 7 is depicted, but without thearray 60. The FIG. 8 further depicts a first coordinate system on thecoordinate axis 60 directed through the both sensor means S0, S1. Thefirst coordinate system, is in this embodiment duplicated, as indicatedthrough the arrows on the axis 62, but as the distance between bothsensor means S0, S1 is fixed only one of the first coordinate systems isneeded for computation.

The movement of the sensor means S0 or S1 (it does not matter which one)in the paper or print medium second coordinate system at an angle‘alpha’ is calculated, in accordance with the present invention, as:deltaX=S0DiffX*cos(alpha)−S0DiffY*sin(alpha)deltaY=S0DiffX*sin(alpha)+S0DiffY*cos(alpha)

Where S0DiffX and S0DiffY are the movements of the sensor means in x-and y-directions respectively, in the sensor/print-head device, namedfirst coordinate system.

The angular change can be calculated as the difference of the sensormeans y-movements in the sensor means first coordinate system multipliedby a constant that is determined from the distance between the sensormeans S0, S1. To simplify, the angle is measured in units of one sensor“step” and the sine and cosine values are taken from tables that areadjusted according to this. Thus S1DiffY−S0DiffY, provides the anglechange.

The movement in x-direction of sensor means S1 is not used, theinformation is redundant since the sensor means geometry is fixed.

When the position of one sensor means S0 or S1 and the tilt angle of thesensor/print head assembly alpha are known the positions of the printhead nozzles can be calculated as follows, depicted in FIG. 7:

The positions of the first and last nozzle are calculated as:PNfirstX=S0x+Ho*cosine(alpha)−Vo*sine(alpha)PNfirstY=S0y+Ho*sine(alpha)+Vo*cosine(alpha)PNlastX=S0x+Ho*cosine(alpha)−Ve*sine(alpha)PNlastY=S0y+Ho*sine(alpha)+Ve*cosine(alpha)

To calculate the positions of all nozzles, it is to start with the firstnozzle positions and adding up the difference in x- and y-directionsbetween the nozzles, calculated by dividing the x- and y-distancebetween the first and last nozzle by the number of nozzles:PN(n)X=PNfirstX+n*deltaXPN(n)Y=PNlast+n*deltaYwheredeltaX=PNlastX−PNfirstYdeltaY=PNlastY−PnfirstY

In accordance with the teaching herein, the present invention sets fortha sensor and ink-jet print-head 2 assembly comprised in a housing 1 fora hand-held and hand-operated printing device controlled by a processor4. It thus comprises:

two position sensor means S0, S1 at least one sensor means being relatedto a first coordinate system, having one axis in a relation to theprint-head assembly, and one axis 62 in a direction through both sensormeans;

a print-head array 60 attached in a fixed position to the sensor meansS0, S1;

input means 6 on the housing connected to the processor for input ofcontrol commands;

determining means for reference coordinates in a second coordinatesystem provided in relation to a print medium, the reference coordinatesbeing established by a control command through the input means 6 withthe thus read sensor means signals;

integrating means for keeping track of the assemblies position relatedto the reference coordinates in the second coordinate system byintegrating displacement of the sensor means position in the firstcoordinate system;

computing means for transforming the sensor means S0, S1 coordinates to

coordinates in the second coordinate system, whereby the assembliesposition on the print medium is determined in relation to the referencecoordinates.

Sensor means and print-heads that are suitable for the present inventionare well known in the art and described in for example U.S. Pat. No.5,927,872 by Yamada, U.S. Pat. No. 6,233,368 B1 by Badyal et al, andU.S. Pat. No. 5,644,139 by Allen et al. Sensor means can be bought fromAgilent, www.agilent.com. Another sensor means has the product nameHDNS-2000 and enables 1.500 pitures/s, the next model in progressenables 6.000 pictures/s. Sensor means in this description can compriseknown means that are to cooperate together with a sensor itself, forexample, LEDs or only be sensors or an array of sensors.

FIG. 9 illustrates an image to be print out with the assembly of thepresent invention, thus stored in the assembly's memory, and FIG. 10depicts a part print out in a random movement accomplished by thepresent invention. An assembly in accordance with the present inventionrelates to Random Movement Printing Technology (RMT).

It is appreciated that the means used in the present invention arehardware means or software means or a combination of both.

The present invention is not restricted to given embodiments orexamples, but the attached set of claims define other embodiments for aperson skilled in the art.

1. A sensor and ink-jet print-head assembly comprised in a housing for ahand-held and hand-operated printing device controlled by a processor,comprising: two position sensors, at least a first sensor being relatedto a first coordinate system, having one axis in a relation to aprint-head array, arranged in a fixed position relative to said sensors,and one axis in a direction through both sensors; at least one inputcontrol on said housing and connected to said processor to input controlcommands; a coordinate determining routine associated with the processorto determine reference coordinates in a second coordinate systemprovided in relation to a print medium, said reference coordinates beingestablished by a control command input through said input control andbased on a sensor signal; a position calculating routine associated withthe processor to track the assembly's position related to said referencecoordinates in said second coordinate system by integrating displacementof at least one sensor position in the first coordinate system; and atransform routine associated with the processor to transform the sensorcoordinates to position coordinates in the second coordinate system,whereby the assembly's position on the print medium is determined inrelation to the reference coordinates, said transform routine beingoperable to derive said transformation of the sensor coordinates,through the position of the first sensor related to the first coordinatesystem and an angle of the print-head array in relation to the secondcoordinate system, and to derive the angle of the print-head array inrelation to the second coordinate system as the difference of the sensormovement in the y-direction of the first coordinate system multipliedwith a constant which is determined in relation to the distance betweenthe two sensors.
 2. An assembly according to claim 1, wherein thetransformation routine is configured to express a position through thesensor coordinates and the angle between the prior sensor position andthe current sensor position.
 3. An assembly according to claim 1,further including a print head position calculating routine associatedwith the processor operable to calculate a print-head nozzle positionfrom one sensor position and the angle of the assembly, by calculatingthe position of a first and last nozzle in said array.
 4. An assemblyaccording to claim 3, wherein the print head position calculatingroutine is operable to calculate remaining nozzle positions by startingfrom the first nozzle positions and adding up the difference in x- andy-directions between the nozzles, whereby the x- and y-distance betweenthe first and last nozzle is divided by the number of nozzles.
 5. Anassembly according to claim 3, wherein the print head positioncalculating routine is operable to calculate remaining nozzle positionsas follows:PN(n)X=PNfirstX+n*deltaXPN(n)Y=PNlast+n*deltaYwheredeltaX=PNlastX−PNfirstYdeltaY=PNlastY−PnfirstY.
 6. An assembly according to claim 1, furtherincluding a print head position calculating routine associated with theprocessor to calculate print-head nozzle positions as follows:PNfirstX=S0x+Ho*cosine(alpha)−Vo*sine(alpha);PNfirstY=S0y+Ho*sine(alpha)+Vo*cosine(alpha);PNlastX=S0x+Ho*cosine(alpha)−Ve*sine(alpha); andPNlastY=S0y+Ho*sine(alpha)+Ve*cosine(alpha).
 7. An assembly according toclaim 1, wherein a width of the assembly is smaller than a width of theprint medium.
 8. An assembly according to claim 1, wherein a positioningguide is provided to position the assembly in a correct startingposition in relation to the print medium.
 9. An assembly according toclaim 1, including an adjustment sensor, wherein a, pattern provided byink-jet drops ejected in even intervals defines reference points toadjust for possible sensor position dislocations, the pattern beingsubstantially invisible to a human eye.
 10. A sensor and ink-jetprint-head assembly comprised in a housing for a hand-held andhand-operated printing device controlled by a processor, comprising: twoposition sensors, at least a first sensor being related to a firstcoordinate system, having one axis in a relation to a print-head array,arranged in a fixed position relative to said sensors, and one axis in adirection through both sensors; at least one input control on saidhousing and connected to said processor to input control commands; acoordinate determining routine associated with the processor todetermine reference coordinates in a second coordinate system providedin relation to a print medium, said reference coordinates beingestablished by a control command input through said input control andbased on a sensor signal; a position calculating routine associated withthe processor to keep track of the assembly's position related to saidreference coordinates in said second coordinate system by integratingdisplacement of sensor position in the first coordinate system; and atransform routine associated with the processor to transform the sensorcoordinates to position coordinates in the second coordinate system,whereby the assembly's position on the print medium is determined inrelation to the reference coordinates, said transform routine beingoperable to calculate the sensor position in the second coordinatesystem at an angle ‘alpha’ as follows:deltaX=S0DiffX*cos(alpha)−S0DiffY*sin(alpha);deltaY=S0DiffX*sin(alpha)+S0DiffY*cos(alpha); and where S0DiffX andS0DiffY are the movements of at least one of the sensors in x- andy-directions respectively, in the first coordinate system.
 11. Anassembly according to claim 10, wherein said transform routine isoperable to derive the angle of the print-head array in relation to thesecond coordinate system as the difference of the sensor movement in they-direction of the first coordinate system multiplied with a constantwhich is determined in relation to the distance between the two sensors.12. An assembly according to claim 10, further including a print headposition calculating routine associated with the processor, operable tocalculate a print-head nozzle position from at least one sensor positionand the angle of the assembly, by calculating the position of a firstnozzle and a last nozzle in said array.
 13. A method for positioncalculation of a sensor and ink-jet print-head assembly comprised in ahousing for a hand-held and hand-operated printing device controlled bya processor, said assembly including two position sensors, whereby atleast a first sensor is related to a first coordinate system, having oneaxis in relation to a print-head array arranged in a fixed position inrelation to said sensors and one axis in a direction through bothsensors, said assembly further including at least one input controlprovided on said housing, the method comprising: determining referencecoordinates in a second coordinate system provided in relation to aprint medium, said reference coordinates being established by a controlcommand through said input control and based on a sensor signals;tracking the assembly's position related to said reference coordinatesin said second coordinate system by integrating displacement of sensorposition in the first coordinate system; and transforming the sensorcoordinates to position coordinates in the second coordinate system,whereby the assembly's position on the print medium is determined inrelation to the reference coordinates, by deriving a transformation ofthe first sensor coordinates, through the position of the first sensorrelated to the first coordinate system and an angle of the print-headarray in relation to the second coordinate system, and deriving an angleof the print-head array in relation to the second coordinate system asthe difference in sensor movement in the y-direction of the firstcoordinate system multiplied with a constant which is determined inrelation to the distance between the two sensors.
 14. A method accordingto claim 13, wherein a position is expressed through the sensorcoordinates and the angle between the prior sensor position and thecurrent sensor position.
 15. A method according to claim 13, furthercomprising computing a print-head nozzle position from at least onesensor position and the angle of the assembly, by calculating theposition of a first nozzle and a last nozzle in said array.
 16. A methodaccording to claim 15, wherein the computing includes computingremaining nozzle positions by starting from the first nozzle positionsand adding up the difference in x- and y-directions between the nozzles,whereby the x- and y-distance between the first and last nozzle isdivided by the number of nozzles.
 17. A method according to claim 16,wherein the computing includes calculating remaining nozzle positions asfollows:PN(n)X=PNfirstX+n*deltaXPN(n)Y=PNlast+n*deltaYwheredeltaX=PNlastX−PNfirstYdeltaY=PNlastY−PnfirstY.
 18. A method according to claim 13, furthercomprising calculating print-head nozzle positions as follows:PNfirstX=S0x+Ho*cosine(alpha)−Vo*sine(alpha);PNfirstY=S0y+Ho*sine(alpha)+Vo*cosine(alpha);PNlastX=S0x+Ho*cosine(alpha)−Ve*sine(alpha); andPNlastY=S0y+Ho*sine(alpha)+Ve*cosine(alpha).
 19. A method according toclaim 13, wherein a width of the assembly is smaller than a width of theprint medium.
 20. A method according to claim 13, further comprisingpositioning the assembly in a correct starting position in relation tothe print medium.
 21. A method according to claim 13, further comprisingejecting ink-jet drops in even intervals as a reference to adjust forpossible sensor position dislocations, said pattern being substantiallyinvisible a human eye.
 22. A method for position calculation of a sensorand ink-jet print-head assembly comprised in a housing for a hand-heldand hand-operated printing device controlled by a processor, saidassembly including two position sensors, whereby at least a first sensoris related to a first coordinate system, having one axis in relation toa print-head array arranged in a fixed position in relation to saidsensors, and one axis in a direction through both sensors, said assemblyfurther including at least one input control provided on said housing,the method comprising: determining reference coordinates in a secondcoordinate system provided in relation to a print medium, said referencecoordinates being established by a control command through said inputcontrol and based on a sensor signal; tracking the assembly's positionrelated to said reference coordinates in said second coordinate systemby integrating displacement of sensor position in the first coordinatesystem; and transforming the sensor coordinates to position coordinatesin the second coordinate system, whereby the assembly's position on theprint medium is determined in relation to the reference coordinates, bycalculating the position of the sensor means in the second coordinatesystem at an angle ‘alpha’ as follows:deltaX=S0DiffX*cos(alpha)−S0DiffY*sin(alpha);deltaY=S0DiffX*sin(alpha)+S0DiffY*cos(alpha); and where S0DiffX andS0DiffY are movements of the sensors in x- and y-directionsrespectively, in the first coordinate system.
 23. A method according toclaim 22, wherein said transforming includes deriving the angle of theprint-head array in relation to the second coordinate system as thedifference in sensor movement in the y-direction of the first coordinatesystem multiplied with a constant which is determined in relation to thedistance between the two sensors.
 24. A method according to claim 22,further comprising computing a print-head nozzle position from at leastone sensor position and the angle of the assembly, by calculating theposition of a first nozzle and a last nozzle in said array.